With the advent of surface modification procedures for the production of fibrillated cellulose, it has become evident that some procedures have a limited negative impact on the cellulose surface chemistry. In the case of TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl)-mediated oxidation, this is evident from the residual aldehyde groups present on the surface and the impact on the colour stability of the resulting material under conditions of high temperature drying. In this paper, an alternative is presented for the common procedure for the oxidation of aldehydes on TEMPO oxidized cellulose using an acidified solution of sodium chlorite. By using potassium peroxymonosulfate, residual aldehyde groups were converted to carboxylic groups, and the colour stability of the modified cellulose fibers was increased. The post-oxidation procedure takes place under mildly alkaline conditions, which preserves the surface charge on the TEMPO modified cellulose fibers, and this in turn helps with fibrillation of the material into a nanofibrillar form.